3 Answers
3

Seeds are not “created”, they are found by trying them. The seed is called that because it is the seed for a pseudorandom number generator which is then used to determine all of the attributes of the world; it is not possible to design a seed to produce a desired result.

Type something for the seed, see if you like the world, and if not, try again with a different seed. Or look for seeds other people have tried; there are many web sites which claim to provide such information.

(However, I note that you mention wanting a superflat world. Superflat is a separately chosen option, not determined by the seed, and Minecraft: Pocket Edition does not have an option for superflat world generation.)

Get pocketinveditor off of for shared. Do edit terrain and click slect whole worl replace blocks then click the top browse button and click air. Then the bottom browse button and click what ever youwant to be super flat like diamonds grass sand stone all of that hope this helped!

Just tried it: does not work. Though blankis a neat half-frozen ocean seed, and there are some impressive mountains and valleys on the edge of the map at one side. It's definitely not super-flat though.
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SevenSidedDieApr 1 '13 at 18:32

This is completely wrong. Leaving the seed blank simply means that Minecraft will use a random seed.
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MBraedleyApr 1 '13 at 19:19